If we are refactoring the HMAC and HKDF crates to behave like the cipher_modes and cipher_padding crates in that it's just a utility crate, but we actually want the types for HMAC_SHA256, HKDF_SHA256, etc to be exposed under the bouncycastle-sha2 crate (and ditto for sha3), then we'll need to refactor to crate docs to reflect that.
If we are refactoring the HMAC and HKDF crates to behave like the cipher_modes and cipher_padding crates in that it's just a utility crate, but we actually want the types for HMAC_SHA256, HKDF_SHA256, etc to be exposed under the bouncycastle-sha2 crate (and ditto for sha3), then we'll need to refactor to crate docs to reflect that.